1. Field of the Invention
This invention relates to stud welding which is a form of electric arc welding. In practice, a stud, a type of metal fastening device, is loaded into an electrically energizable collet, which is usually situated in the barrel of a stud welding tool (gun), grasped and positioned over an area of attachment, more commonly referred to as a work piece or a work area. When the tool is energized, an arc is created between the distal end of the stud and the area of attachment on the metal work piece. The arc melts the distal tip of the stud and the attachment site on the work piece. A timing device in the tool determines the duration of the arc and, when completed, the tool plunges the stud into the molten pool at the area of attachment creating a weldment to the work piece.
There are several reasons for developing an adjustable collet. The most apparent, of course, is versatility. The welder should be able to select and use any reasonably sized or shaped stud to effect optimal fastening. The size and accessibility of the stud should not be dictated by the size or maneuverability of the collet. Therefore, a collet that can be opened and adjusted to access and accommodate a variety of different sized and shaped studs would provide a definite work place advantage.
Furthermore, with the traditional cylinder-shaped collet providing a xe2x80x9cfinger-fitxe2x80x9d for a stud of a particular shape and size, it is not uncommon for premature wear and arcing to combine to shorten the useful life of the collet and, over time, as the collet deteriorates, to deliver welds of diminished quality. With a fixed collet there is, understandably, more wear on the collet simply as a result of the abrasive movement of the stud into the collet and the withdrawal of the collet from the welded stud. This repetitive movement will abrade the inner surface of the traditional fixed collet, weaken any tensioning means for holding the stud and result in a loose fit and, over time, permit little more than haphazard contact between the collet and the stud. Anything less than a snug fit ensuring secure contact between the collet and the stud will increase the likelihood of peripheral arcing and jeopardize the intensity and quality of the arc to be created between the distal tip of the stud and the work surface. This peripheral arcing, in time, also causes more wear, thus more arcing; and, before long, the useful life of the traditional collet is finished and a replacement needs to be installed.
Most collet manufacturers haven""t been highly motivated to address the problem of fixed-collet deterioration. However, some patent references have made suggestions for prolonging collet life and increasing versatility.
2. Description of the Prior Art
Generally, a collet for the attachment of studs to a work piece is a tubular electrode, used in combination with a stud welding gun designed to hold weld studs in proximity to the area of attachment prior to welding. Traditionally, these tubular electrodes are heavy-walled and machined to provide a plurality of close-tolerance xe2x80x9cfingersxe2x80x9d at the end of the collet for gripping the stud and providing a modicum of flexiblity.
U.S. Pat. No. 4,027,136 to Taylor describes an automatic welding device with what is alleged to be an improved collet design that is relatively easy and inexpensive to manufacture. It features slots and flexible xe2x80x9cfingersxe2x80x9d for gripping the stud and a reduced frontal surface area to minimize the collection of splatter material from the welding process, and thereby diminish the likelihood of undesirable arcing.
U.S. Pat. No. 4,163,888 to Ettinger describes an arc welding device with a stud gripping collet. The lower end of this collet has a plurality of spring-like xe2x80x9cfingersxe2x80x9d which receive and grip the stud while the upper end of the collet is provided with internal threads for receiving an adjustment screw which may be moved in or out of the collet to adjust the length of that portion of the stud extending from the collet so that studs having various lengths can be used in the described device.
The instantly disclosed adjustable collet is distinguished from and improves upon the devices of the prior art by providing an adjustable collet designed to be used for welding studs having a variety of shapes and dimensions and presented in orientations that may or may not complicate attachment to the work piece. The adjustable collet comprises a plurality of electrically energized jaws, each having at least one surface for contacting the stud to be welded, and an adjusting means, in association with the jaws, for opening and closing the jaws and holding the stud between each of the contacting surfaces.